Field of the Invention
The present invention relates to a pneumatic tire that is excellent in drainage performance.
Background Art
In a pneumatic tire (hereinafter, referred to as “tire”), it is important to assure drainage performance for suppressing hydroplaning phenomenon which may occur when the vehicle is moving especially at a high speed, in which a water film is built up between the tire tread and the road surface, thereby causing the tire to lose total or partial contact with the road surface and hence causing the tire to ride on the water film on the road surface.
Grooves are formed in the tire tread in order to channel water flow caused due to the rotation of tire and hence assure the water drainage. Here, when grooves having a rectangular cross section are formed, the necessity to form a wide groove is caused in order to secure the groove volume, which results in a problem of decreasing the tire rigidity. When the inner side surface of each groove is formed to be inclined (flattened), the width of the groove bottom can be decreased while securing the same groove volume as that of the groove having the rectangular cross section so that the tire rigidity can be relatively improved. However, there is no substantial difference in respect of water drainage performance between those grooves. Further, as described in JP 2010-184570 A, when the groove's inner side surface is formed to be curved, the groove volume can be increased by the curved inner side surface as compared with the groove having the inclined flat inner side surface. However, such curved inner side surface causes vortex flow due to water flowing along the curved inner side surface, which prevents smooth water drainage.